GB2306495A - Composite materials - Google Patents

Abstract

A composite material for example for use in making shower trays comprises water extended polyester resin, water and mineral filler. The water reduces the amount of resin and permits casting of lighter weight trays without excessive exotherm. The amount of water is 40-200 parts (by wt) per 100 parts resin, and that of filler 30-1000 parts per 100 parts water and resin.

Description

COMPOSITE MATERIALS The present invention concerns composite materials.

It is well known that the use of mineral and other fillers with polyester and other resins can create cast material known as polymer concrete. Such materials rely on a mixture of fillers and aggregates which, with an appropriate amount of resin binder, will offer good strength coupled with speed of manufacture and, in some cases, chemical resistance. An aggregate is a form of filler which is typically of larger particulate size.

It is also known that polyester resin may be processed in such a way as to be capable of emulsification with water, such systems, known as WEP (Water Extended Polyester) sometimes referred to as WFP (Water Filled Polyester), are used in limited areas such as decorative castings but are not regarded as suitable for use as engineering materials due to a tendency to shrink as the contained water dries out and thus become weak and friable.

The resins may consist of unsaturated polyester resin formed by a condensation polymerisation reaction which is allowed to proceed until the polyester has an acid value greater than 25 and contains more than 30 per cent of unsaturated monomer by weight.

The term filler is leased herein to include aggregate.

According to the invention a composite material comprises a water extended polyester resin, water and mineral filler, the amount of water being from 40 to 200 parts per hundred of resin by weight and the amount of filler is from 30 to 1000 parts by weight to one hundred parts of water and resin combined.

The proportion of resin may be between 5 and 10 per cent by volume e.g. between 10 and 15 per cent by volume.

One example provides a polymer concrete or composite material based on water extended polyester resin in which the fillers and aggregates overcome the basic tendency of water extended polyester resins to be weak and friable, and by virtue of the water extension, contain substantially reduced volume fractions of resin compared to conventional polymer concrete.

The weight of resin includes the weight of catalyst.

During experiments on resins with fillers/aggregates intended for use as fire resistant panels it was decided that a major advantage in terms of fire performance could be gained by a reduction in resin content in the composite. Since the resin is used both as the binder and also as the vehicle in respect of flow during casting, it was considered that water filled resins may offer a means of assisting flow using a non-combustible fluid (water).

The results were surprisingly good, with the WEP resin system allowing substantial reduction in resin content whilst retaining good castability, and with the high volume fractions of fillers and aggregates substantially reducing levels of shrinkage.

At the same time, there was no indication that the castings so produced were substantially inferior to similar systems using resins which were not water extended. It is assumed that it is the high level of fillers and aggregates which effectively 'reinforces' the composite by preventing the shrinkage which is normally associated with this type of cast resin system.

The composite mixtures claimed may be formed into various shapes by methods which include but are not limited to casting, pressing, extrusion, pultrusion, resin transfer, and spraying.

Uses in view include, but are not limited to, access flooring panels, garden furniture and planters, fire resistant panels, resin bonded shower trays and various building products.

The polymer concrete of the present invention can also be used in formulations which are applied in applications such as stiffening of acrylic and grp (fibreglass reinforced plastics) mouldings (e.g. bath tubs), fibre glass pool manufacture, glass fibre signs manufacture.

Conventionally such stiffening applications rely on resin and glass fibre alone with the occasional use of mineral fillers to reduce cost or to improve opacity, colour or fire retardance.

The water extension of the resin reduces cost by the creation of thicker layers of material for a given amount of resin and which are thus inherently stiffer than before and which require less glass fibre to be used as stiffening with a consequent reduction in weight and cost.

The fillers and aggregates referred to above include but are not limited to conventional materials such as sands and shingles, crushed limestone, dolomite, slate and other naturally occurring minerals, and manufactured materials such as lightweight expanded clay aggregates, expanded perlite, exfoliated vermiculite, foamed clay pellets, fly ash, foamed glass.

The systems designed to be fire resistant may be entirely or partly filled with minerals which provide fire retardant properties such as alumina trihydrate, magnesium carbonate gypsum.

For strength the systems may be reinforced with glass or other fibres, mica or other lamellar minerals.

The use oY water extended polyester resin in shower trays has great significance in the development of that product.

To date, the development of shower trays has gone through a series of stages dependent on the available technology for their manufacture. The individual stages which are of interest here are the early trays which were ceramic and the almost simultaneous development of steel trays. These developments followed the conventional development of sanitary ware.

There then followed, on the same basis, the acrylic trays based on the development of acrylic baths, where the main shape and colour requirements are met by use of vacuum moulded acrylic sheet and the stiffness was provided by reinforcement with glass reinforced polyester resin or chipboard or both.

All of these types of shower tray are still in production but are rapidly being replaced by resin bonded (polymer concrete) materials. There are still, however, certain difficulties which have yet to be overcome if the manufacture of trays is to advance further in terms of wide availability in particular the high weight which is given by polymer concrete.

Given the advanced state of the use of lightweight fillers and aggregates in composites it would be expected that there would be a simple means of reducing the specific gravity of these formulations. In fact, the attempts so far to reduce weight by that method have revealed a major problem namely high temperatures in the moulds caused by the exothermic reaction of the resin systems, frequently followed by cracking of the mouldings by thermal contraction following the high moulding temperatures. In extreme cases there has also been damage to the moulds.

The reasons for this high temperature is believed to be the reduced thermal capacity of the fillers when lightweight aggregates are used. The lightweight fillers and aggregates have similar specific heat to the conventional dense fillers and aggregates used in this application and there is bound to be a higher temperature reached for a given amount of energy developed during exotherm when that exotherm is acting on a lower mass of filler material.

There is also a tendency for lightweight materials to not flow so easily as heavy materials, requiring the use of increased resin concentrations to promote flow and thus further increasing the level of exotherm.

The insulating effect of the fillers is also frequently blamed for this problem but the effect of insulation generally is to make temperature more even throughout the mouldings and probably contributes to less differential cure rates across differing thickness of cast material.

According to another arrangement there is provided a material for casting shower trays and other similar mouldings in which the resin is extended with water as a means of reducing exotherm so as to allow the cost of normal weight trays to be reduced and to allow the casting of lightweight trays without excessive exotherm.

By using the WEP system it is possible to make two significant alterations in the curing process. Firstly, the resin content is reduced with a substantial reduction in cost and potential exotherm.

Secondly, the water has a much higher specific heat than mineral fillers and thus absorbs the exotherm with a lower rise in temperature.

The amount of the addition of water is dependent on the fillers to be used and the degree of filling envisaged, but would be in the range of 40 to 200 parts per hundred of resin by weight.

In the case of tests on shower trays a one to one by weight ratio of water and resin has been used.

This provides an adequate balance at this stage between minimising resin content but maintaining the ability of the system to adhere to gel coats.

If gel coats are not to be used, up to 200 parts water per hundred of resin by weight can be used or, where there is a need for improved bonding, the water content may be reduced below 100 parts per hundred parts of resin by weight.

The water is required on four counts.

1. It reduces cost by providing the vehicle by which a material may be rendered castable without the high cost of additional resin, and 2. It reduces the potential exotherm of the system by reducing the volume fraction of resin, and 3. It provides a heat sink to replace that lost when heavy fillers are replaced by lightweight fillers thus absorbing the exotherm produced with a lower rise in temperature.

4. The reduced resin content provides better dimensional stability in the composite as shown by the lack of distortion during cure.

Examples 1. A typical casting system for the production of shower trays would consist of five to one by weight mixture of fillers to resin and would thus contain a volume fraction of resin between 25 and 30 percent by volume of resin.

2. A WEP casting formulation with equivalent rheology would contain the same ratio of filler to fluid ratio but the fluid would now consist of resin and water combined with the effect of reducing the typical resin content in the composite to less than fifteen percent.

3. A typical floor tile formulation would consist of the same filler to fluid ratio as 2. but would contain mainly larger aggregates and fillers.

4. In a simulated slate application the filler to fluid ratio would be as in 2. and would require the water to moderate the exotherm and thus protect the integrity of the slate during microwave curing.

The contained water acts as a means of postcuring the slates by allowing the use of microwave more effectively to raise their temperature after initial cure.

In this application there are the additional benefits of lowering resin content by using WEP namely improvement in heat distortion temperature of the slate, and improved slate-like appearance due to the 'non-resinous' appearance of heavily filled water extended polyester resin.

FILLER CONTENT OF WEP SYSTEMS Filler loading may be in the range of 30 to 1000 parts by weight to one hundred parts of emulsified resin/water depending on the density of the fillers and the level of filling required.

EXAMPLES 1. Using 5.25 litres (approximately 5.78 kilos) conventional polyester casting resin, 90 centilitres of MEKP (methylethylketone peroxide) catalyst and 29 kilos of pre-blended mineral fillers were added. The whole was mixed using a modified concrete mixer until homogeneous. This mixture was then cast into a gel-coated shower tray mould and vibrated until level. The mixture heated up due to the reaction of the resin and became hard and was demoulded after 90 minutes. Calculations of the resin and filler content in this moulding show the following results: % by volume Resin 30.96 Water 00.00 Filler 69.04 Composite density 2.24 2. Using 3 kilos water extendible polyester resin, three kilos of water were added while mixing with a high shear mixer.To the emulsified resin/water were added 60ccs of MEKP catalyst and 29 kilos of pre-blended mineral fillers and the whole mixed in a modified concrete mixer until homogeneous. This mixture was then cast into a gel-coated shower tray mould and vibrated until the material was level. The exotherm was much less than in example 1, but the shower tray was demoulded in 90 minutes and was a good moulding.

Calculations of the resin and filler content in this moulding show the following results: % by volume Resin 12.55 Water 15.06 Filler 72.39 Composite density 1.76 3. Using 3 kilos water extendible polyester resin, three kilos of water were added while mixing with a high shear mixer. To the emulsified resin/water were added 90ccs of MEKP catalyst and 10 kilos of lightweight mineral fillers and the whole mixed in a modified concrete mixer until homogeneous. This mixture was then cast into a gel-coated shower tray mould and vibrated until the material was level. The exotherm was much more apparent than in example 2, and the shower tray was demoulded in 90 minutes and was a good moulding. Calculations of the resin and filler content in this moulding show the following results: % by volume Resin 14.84 Water 17.81 Filler 67.35 Composite density 0.98 4.Using 1 kilo of conventional polyester casting resin, there was added 100 centilitres of MEKP catalyst and 8 kilos of blended fillers and the whole mixed by hand. This mixture was then cast into slate moulds and allowed to cure. Calculations of the resin and filler content in this moulding show the following results: % by volume Resin 21.95 Water 00.00 Filler 78.05 Composite density 2.37 5. Using 0.5 kilos of water extendible polyester resin 0.5 kilos of water were added while mixing with a high shear mixer.

There was then added 10 centilitres of MEKP catalyst and 2.5 kilos of blended mineral fillers and the whole mixed by hand. This mixture was then cast into slate moulds and allowed to cure. Calculations of the resin and filler content in this moulding show the following results: % by volume Resin 12.39 Water 14.36 Filler 72.75 Composite density 2.16 6. Using 2 kilos water extendible polyester resin, two kilos of water were added while mixing with a high shear mixer. To the emulsified resin/water were added 40ccs of MEKP catalyst and 10.5 kilos of mixed heavy and lightweight mineral fillers and the whole mixed in a modified concrete mixer until homogeneous. This mixture was then cast into a gel-coated access floor tile mould and vibrated until the mould was full and the material level.The tile was demoulded in 50 minutes and was a good moulding with excellent adhesion to the gel-coat and to the galvanised steel tray.

Calculations of the resin and filler content in this moulding show the following results: % by volume Resin 13.16 Water 15.80 Filler 71.04 Composite density 1.25 7. Using the procedure in example 4 a moulded slate was then subjected to microwave as a means of accelerating the cure.

The temperature of the slate was raised to 65 degrees Celsius and the slate was demoulded after one minute. The slate was split into two halves and one half subjected to a further dose of microwave to raise its temperature to 95 degrees Celsius. The residual styrene content of the slate prior to the further treatment was measured and shown to be 0.5 per cent. The residual styrene content of the slate after postcuring with microwave at 135 degrees Celsius was shown to be 0.03 per cent.

8. Using 2 kilos water extendible polyester resin, two kilos of water were added while mixing with a high shear mixer. To the emulsified resin/water were added 40ccs of MEKP catalyst and 1.2 kilos of mixed ultra-lightweight mineral fillers and the whole mixed in a modified concrete mixer until homogeneous. This mixture was then cast into a flat panel mould and allowed to cure. This resulted in a very lightweight panel. Calculations of the resin and filler content in this moulding show the following results: % by volume Resin 14.85 Water 17.82 Filler 67.32 Composite density 0.46 9. Using 2 kilos water extendible polyester resin, two kilos of water were added while mixing with a high shear mixer. To the emulsified resin/water were added 40ccs of MEKP catalyst and 20 kilos of mixed ultra-heavyweight mineral fillers and the whole mixed in a modified concrete mixer until homogeneous.This mixture was then cast into a flat panel mould and allowed to cure. This resulted in a very heavy panel. Calculations of the resin and filler content in this moulding show the following results: % by volume Resin 12.53 Water 15.03 Filler 72.44 Composite density 3.31 10. In a further example, limestone filler/water/resin are present in parts by weight in amounts 1000/40/100 (total 1140) and in percentage by volume 75/8/17. The resin % by weight is 8.8.

11. In another example with limestone filler/water/resin the proportion is 1500/200/100 by weight (5.6% resin) and 66/24/10 % by volume.

12. In a further example with ceramic aggregate (e.g. that sold under the name Tecpril) the proportion is 55/200/100 by weight, 66/24/10 % by volume.

It will be noted that the resin content of examples 2, 3, 5, 6, 8 to 12 according to the invention are less than 20% by volume typically less than 15%; the resin content of examples 1,4 using unextended resin is over 20%.

A shower tray size 760mm square by 150mm tall made by conventional means may weigh typically 30 to 40 kilos; a shower tray made using material according to the invention typically weighed 20 kilos or less.

Claims (3)

1. A composite material comprising water extended polyester resin, water and mineral filler, the amount of water being from 40 to 200 parts per hundred of resin by weight and the amount of filler being from 30 to 1000 parts by weight to one hundred parts of water and resin combined.

2. A composite material as claimed in Claim 1 and substantially as hereinbefore described.

3. A shower tray formed of composite material as claimed in any preceding claim.